The present invention relates to the general field of fastening equipment on a composite material structure.
One of the fields of application of the invention is that of composite material fan casings for gas turbines of aeroengines, which casings have various pieces of equipment mounted thereon.
In a gas turbine aeroengine, a fan casing performs several functions. It defines the air inlet passage into the engine, it supports an abradable material facing the tips of the blades of the fan, it supports an optional soundwave absorber structure for performing acoustic treatment at the inlet of the engine, and it incorporates or supports an optional shield for retaining debris.
It has become common practice to fabricate a fan casing out of composite material, in particular by a technique of injecting resin under a vacuum (also referred to as resin transfer molding (RTM)). In that fabrication technique, a fiber preform is wound in superposed layers on a winding mandrel forming an injection mold. Once the mold has been closed, a thermosetting resin is injected into the inside of the mold and then polymerized. The fan casing is unmolded after it has cooled. Reference may be made to document EP 1 961 923, which describes an implementation of such a method.
A fan casing also supports various pieces of equipment, such as for example flanges for holding pipework and supports for accessories (probes, etc.). This equipment is generally mounted against one of the faces of the casing merely by means of fastener screws. Unfortunately, that type of assembly is not strong because of the poor holding power of the threads made in the composite material into which the fastener screws are screwed (in particular compared with tapping made in a metal material). Having recourse to bushings screwed into the fan casing does not enable that problem to be solved, since putting such bushings into place likewise requires holes formed in the composite material to be tapped.